The following description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art, or relevant, to the presently claimed inventions, or that any publication specifically or implicitly referenced is prior art.
The eukaryotic heat shock protein 90s (HSP90s) are ubiquitous chaperone proteins that are involved in folding, activation and assembly of a wide range of proteins, including key proteins involved in signal transduction, cell cycle control and transcriptional regulation. Researchers have reported that HSP90 chaperone proteins are associated with important signaling proteins, such as steroid hormone receptors and protein kinases, including, e.g., Raf-1, EGFR, v-Src family kinases, Cdk4, and ErbB-2 (Buchner J., 1999, TIBS, 24:136-141; Stepanova, L. et al., 1996, Genes Dev. 10:1491-502; Dai, K. et al., 1996, J. Biol. Chem. 271:22030-4). Studies further indicate that certain co-chaperones, e.g., Hsp70, p60/Hop/Sti1, Hip, Bag1, HSP40/Hdj2/Hsj1, immunophilins, p23, and p50, may assist HSP90 in its function (see, e.g., Caplan, A., 1999, Trends in Cell Biol., 9: 262-68).
Ansamycin antibiotics derived from Streptomyces hygroscopicus are known to inhibit HSP90s. These antibiotics, e.g., herbimycin A (HA) and geldanamycin (GM), as well as other HSP90 inhibitors such as radicicol, bind tightly to an N-terminus pocket in HSP90 (Stebbins, C. et al., 1997, Cell, 89:239-250). This pocket is highly conserved and has weak homology to the ATP-binding site of DNA gyrase (Stebbins, C. et al., supra; Grenert, J. P. et al., 1997, J. Biol. Chem., 272:23843-50). Further, ATP and ADP have both been shown to bind this pocket with low affinity and to have weak ATPase activity (Proromou, C. et al., 1997, Cell, 90: 65-75; Panaretou, B. et al., 1998, EMBO J., 17: 4829-36). In vitro and in vivo studies have demonstrated that occupancy of this N-terminal pocket by ansamycins and other HSP90 inhibitors alters HSP90 function and inhibits protein folding. At high concentrations, ansamycins and other HSP90 inhibitors have been shown to prevent binding of protein substrates to HSP90 (Scheibel, T., H. et al., 1999, Proc. Natl. Acad. Sci. USA 96:1297-302; Schulte, T. W. et al., 1995, J. Biol. Chem. 270:24585-8; Whitesell, L., et al., 1994, Proc. Natl. Acad. Sci. USA 91:8324-8328). Ansamycins have also been demonstrated to inhibit the ATP-dependent release of chaperone-associated protein substrates (Schneider, C., L. et al., 1996, Proc. Natl. Acad. Sci. USA, 93:14536-41; Sepp-Lorenzino et al., 1995, J. Biol. Chem. 270:16580-16587). In either event, the substrates are degraded by a ubiquitin-dependent process in the proteasome (Schneider, C., L., supra; Sepp-Lorenzino, L., et al., 1995, J. Biol. Chem., 270:16580-16587; Whitesell, L. et al., 1994, Proc. Natl. Acad. Sci. USA, 91: 8324-8328).
This substrate destabilization occurs in tumor and non-transformed cells alike and has been shown to be especially effective on a subset of signaling regulators, e.g., Raf (Schulte, T. W. et al., 1997, Biochem. Biophys. Res. Commun. 239:655-9; Schulte, T. W., et al., 1995, J. Biol. Chem. 270:24585-8), nuclear steroid receptors (Segnitz, B., and U. Gehring. 1997, J. Biol. Chem. 272:18694-18701; Smith, D. F. et al., 1995, Mol. Cell. Biol. 15:6804-12), v-src (Whitesell, L., et al., 1994, Proc. Natl. Acad. Sci. USA 91:8324-8328) and certain transmembrane tyrosine kinases (Sepp-Lorenzino, L. et al., 1995, J. Biol. Chem. 270:16580-16587) such as EGF receptor (EGFR) and Her2/Neu (Hartmann, F., et al., 1997, Int. J. Cancer 70:221-9; Miller, P. et al., 1994, Cancer Res. 54:2724-2730; Mimnaugh, E. G., et al., 1996, J. Biol. Chem. 271:22796-801; Schnur, R. et al., 1995, J. Med. Chem. 38:3806-3812). The ansamycin-induced loss of these proteins leads to the selective disruption of certain regulatory pathways and results in growth arrest at specific phases of the cell cycle (Muise-Heimericks, R. C. et al., 1998, J. Biol. Chem. 273:29864-72), and apoptsosis, and/or differentiation of cells so treated (Vasilevskaya, A. et al., 1999, Cancer Res., 59:3935-40).
Growth arrest of this sort, provided it can be made selective, has important ramifications for the treatment of proliferative diseases, i.e., cancers. Whereas cancer treatments have thus far been limited to traditional surgical removal, radiation, and/or chemotherapy, and whereas these procedures have been more or less successful, a need remains to develop additional therapies with increased efficacy and decreased side-effects. There particularly remains a need for cancer treatments that target specific cancer types, e.g., those characterized by the overexpression of Her-2/neu.
The Her-2/neu oncogene, also called erbB2, encodes a glycoprotein with tyrosine kinase activity known as p185 (Schechter, A. L. et al., 1984, Nature, 312: 513-516). HER-2 is a member of the epidermal growth factor receptor (EGFR) family and shares partial homology with other family members. In normal adult tissues, HER-2 expression is low; however, HER-2 is reported to be overexpressed in many tumors, including a significant fraction of human tumors of the breast, lung, ovary, and pancreas (Hynes, N. E. and Stern, D. F., 1994, Biochem. Biophys. Acta., 1198: 165-184.) Studies indicate that HER-2 is overexpressed in at least 25-30% of breast cancers (McGuire & Greene, 1989, Semin. Oncol. 16: 148-155). Furthermore, overexpression of HER-2 in malignant breast tumors is correlated with increased metastasis, chemoresistance and poor survival rates (Slamon et al., 1987 Science 235: 177-182).
Because HER-2 overexpression is associated with and contributes to many types of mammalian proliferative diseases, a means of controlling such overexpression is much needed. A treatment that could simultaneously avoid or minimize harm to normal cells and tissues would be most desirable. The present invention satisfies these needs and provides related advantages as well.